Export LFMCMC

[gvegayon]

We need the following:

• Create a wrapper that exports LFMCMC<> object to R (under src/ and the corresponding wrapper in R under R/ that should be exported with #' @export).
• Create wrapper methods that allow calling the methods in LFMCMC<> from within R.
• Create an example using the SIR model as featured here as a Vignette.

Ideal usage in R:

library(epiworldR)

observed_cases <- read.csv(...)

model <- ModelSIR(...)

mycalib <- LFMCMC() |>
  set_kernel_fun() |> # is using a default, for now
  set_model(model) |> # This is mimicking set_simulation_fun and set_summary_fun in one step
  set_proposal_fun() |> # Use default for now
  set_observed_data(observed_cases)

calibrate(mycalib)

summary(mycalib)